Cathodes with treated apertures for interconnecting gas cells of a display panel

ABSTRACT

A display panel including a lower layer and an upper layer of gas-filled cells with cathodes in common between the layers and with separate anodes associated with each layer of cells, tiny apertures in the cathodes interconnecting upper and lower cells, having improved cathodes wherein the surfaces in the apertures of the cathodes are treated to increase their work function so that these surfaces do not support cathode glow in the operating conditions of the panel, thus preventing spurious transfer of cathode glow from the lower scanning to the upper visible layer of cells.

United States Tatent Glaser [54] CATHODES WITH TREATED APERTURES FOR INTERCONNECTING GAS CELLS or A DISPLAY PANEL [72] Inventor: David Glaser, Bound Brook, NJ.

[73] Assignee: Burroughs Corporation, Detroit,

Mich.

[22] Filed: Feb. 26, 1970 211 Appl. No.: 14,368

[52] US. Cl. ..315/l69 TV, 313/201, 313/220, 315/58 [51] Int. Cl. ..H05b 37/00 [58] Field of Search ..313/20l, 220; 315/58, 169, 315/169 TV [56] References Cited UNITED STATES PATENTS Schwartz ..315/169 X LHeureux ..313/220 X O'Meara ..3l5/58 X [151 3,693,046 1 Sept. 19,1972

2/1943 Van Geel et a1. ..313/l06 X 2,310,002 2,417,730 3/1947 Becker ..,...3l3/106 X 3,389,285 6/1968 Thompson ..3l3/106 X Primary Examiner-Roy Lake Assistant Examiner-Lawrence J. Dahl Attorney-Kenneth L. Miller and Charles S. Hall [57] ABSTRACT A display panel including a lower layer and an upper layer of gas-filled cells with cathodes in common between the layers and with separate anodes associated with each layer of cells, tiny apertures in the cathodes interconnecting upper and lower cells, having improved cathodes wherein the surfaces in the apertures of the cathodes are treated to increase their work function so that these surfaces do not support cathode glow in the operating conditions of the panel, thus preventing spurious transfer of cathode glow from the lower scanning to the upper visible layer of cells.

4 Claims, 4 Drawing Figures PATENTED E 19 19 2 3.6 93, 046

' sum 1 or 2 Q mvnmon DAVID GLASER pp 50 m ATTORN E\ CATHODES WITH TREATED APERTURES FOR INTERCONNECTING GAS CELLS OF A DISPLAY PANEL BACKGROUND OF THE INVENTION Display panels comprising a plurality of gas-filled cells which can be turned on selectively to display a message are known in the art, but have thus far not become widely used commercial devices. In a recent development, a display panel has been invented having two layers of cells and utilizing cathodes in common between the layers. The cathodes are usually in the form of parallel metal strips, each having across its length a row of tiny apertures interconnecting the gas cells in the upper and lower layers, thus forming an array of such apertures. The lower layer of cells is continuously scanned to maintain acathode glow on the lower surface of the cathodes around the apertures. As information signals are applied to anodes of the upper layer of cells, synchronously with the scanning, the

cathode glow spreads to the front surface of the cathode at the selected cell or cells to form a visible unit of a display.

In the prior art the maintained glow on the lower surface of the electrodestended to extend onto the inner surfaces of the tiny apertures. Under customary conditions this glow in the aperture was not visible. However, in case of minor irregularity in the size of the aperture, or under certain conditions 'of current density in the scanning operations, the otherwise invisible glow may spread into thedisplay cell to form a spurious glowing dot in the display.

It is, therefore, the object of this invention to stop the spread of glow inadvertently from a scanning cell to a display cell in a double layer gas-cell display panel.

SUMMARY OF THE INVENTION In accomplishing the above object, applicant has invented a method for preventing spurious spread of glow from the lower scanning gas cell to the upper visible gas cell of an array of such cells in a two layer gas cell display panel through the tiny aperture in the common cathode'between the upper and lower cells by treating the inner surfaces of the aperture by increasing their work function, as with a thin layer of insulation, whereby such treated surfaces will not support cathode glow in the operating conditions of the cell, and the resulting article of manufacture.

DESCRIPTION OF THE DRAWINGS For a more complete understanding of the method and article of manufacture of the invention, reference may be made to the following detailed description, in conjunction with the drawings wherein:

FIG. 1 is an exploded view of the displaypanel in which the treated cathodes of the invention are embodied;

FIG. 2 is a cross section of the display panel taken along the line 2-2 of FIG. 1;

FIG. 3 is another cross section of the display panel taken along the line 3-3 of FIG. 2; and

FIG. 4 is an enlarged view of a portion of FIG. 3 showing the treated surface of a cathode aperture in the display panel.

DESCRIPTION OF THE PREFERRED EMBODIMENT The display panel described herein is a thin, flat, sheet-like member which may have substantially any desired size and shape from, for example, postage stamp size to wall size, and it may include an array of substantially any number of cells. The panel may also include any suitable ioni'zable gas such as neon, argon, xenon, etc., singly or in combination, with a vapor of a metal, such as mercury, which is usually included in the gas to minimize cathode sputtering.

A display panel 10 embodying the invention includes a bottom plate 20 of an hermetic, dielectric material, such as glass or ceramic, which has a top surface 30 in which a plurality of parallel slots 40 is formed. For purposes of this description, the slots are considered to be oriented horizontally. First electrodes 50, which are operated as scanning anodes in onemode of operation of the panel, are preferably in the form of wires, and are seated in the slots 40. r

The panel 10 also includes second electrodes 70,

used as cathodes, and seated on the top surface 30 of i the base plate 20; The cathode electrodes are parallel to each other, and are oriented generally vertically and perpendicular to the anode electrodes 50. Each cathode electrode crosses each anode wire, and each crossing defines a counting or scanning cell 60, as shown in FIG. 3. Each cathode, in conjunction with the anode wires it crosses, thus defines a column of cells 60. The cathode electrodes 70 are preferably relatively wide metal strips, and each has a plurality of tiny apertures aligned along its length, each aperture being located over an anode wire in a slot 40 beneath it. The apertures 80 are preferably not more than 3 mils in diameter.

According to the invention, referring to FIG. 4, the cathode electrodes 70 are constructed or treated so that the surfaces in apertures 80 have a different, higher work function than the top and bottom surfaces, 71 and 72, of the cathodes. Thus, the breakdown potential of the surfaces in the holes is higherthan that of the top and bottom surfaces so that the cathode glow takes place preferentially on the top and bottom surfaces and not in the apertures. To achieve this result, the metal surface in each aperture is oxidized, or otherwise processed, to achieve the desired condition.

Referring back to FIGS. 1-3, an insulating center plate of glass, ceramic, or the like is seated on plate 20 and cathode electrodes 70. Plate 110 has a plurality of apertures arrayed in rows and columns, with each aperture 120 generally vertically aligned with an aperture 80 in a cathode 70 and with a scanning cell 60. Each column of apertures 120 is thus alignedwith and overlays a column of scanning cells 60.

Third electrodes 130, operated as anode electrodes and preferably wires, are seated on the top surface 140 of the apertured plate 110 or in slots (not shown) in the top surface 140. The anode electrodes are oriented parallel to and are aligned with the lower anode electrodes 50, and each is aligned with a row of apertures 120 is plate 110. Each portion of an anode 130 aligned with an aperture 120 and the portion of cathode 70 beneath it comprises a display cell 136 is the panel 10.

A glass cover plate 150 completes the panel 10, and, in the completed panel, the plates 20, 110, and 150 are sealed together at their edges, for example, by means of a fused glass frit, which forms a seal 160, shown in FIGS. 2 and3.

The operation of multi-cell display panels such as panel is described in detail in the co-pending application of Ogle and H012 Ser. No. 850,984, and reference is made to that application for a complete discussion of such operation. Briefly, in one mode of operation of panel 10, the lower cells 60 are continuously scanned column-by-column by the sequential energization of the cathodes 70 and all of the anodes 50, and glow is produced in each column of cells 60 in turn. This sequential scanning of the cells 60 is continued at a rate to maintain cathode glow on the lower surfaces of the cathodes 70 around the apertures 80 of the cells 60.

Simultaneously with the scanning, and synchronously with the scanning rate, information signals are applied to the upper anode electrodes 130, and, where the information signals dictate, glow is transferred upwardly from scanning cells 60 into display cells 136. The intensity of glow in the display cells is determined by the level of the information signals. As the panel is scanned, and information signals are applied, a stationary but changeable display or message is visible through the top plate 150.

The voltage and current conditions of the scanning cells are adjusted to maintain a low level cathode glow in each scanning cell around its aperture 80. As set out fully in Ser. No. 850,984, referred to above, this condition is preferably achieved by maintaining the scanning anodes at substantially +250 volts and the cathode normally at +100 volts with a scanning pulse at close to ground potential. The information (upper) anodes may have a normal voltage of +1 30 volts, for example, with information pulse of +250 volts.

If the diameter of the apertures 80 is kept quite small, for example, not more than 3 mils, the voltage differential between the top surface of the cathode and the scanning anode is normally not sufficient to cause cathode glow on the top of the cathode unless an information pulse is present. However, it has been found quite expensive to form all these tiny apertures with adequate precision. In addition, there may be small variations of voltage and current conditions. Either a variation in aperture diameters or circuit condition abnormality may be sufficient to cause at least some cathode glow in the display area without a concurrent information pulse.

The present invention lies in the discovery that spurious cathode glow does not spread to the display surface of the cathodes 70 if the inner surface 81 of these apertures 80 is treated to have a higher work function than the upper and lower surfaces 71, 72. Under these conditions the inner surface of the aperture does not support cathode glow under the working conditions of the cell and there is no tendency for the glow to spread into this area. The treated area appears to act as a barrier which restrains the spread of cathode glow directly from the lower surface 72 to the upper surface 71 of the cathode 70 under the conditions described above.

To achieve this difference in work function between he' rsurf 81 fth 80 dt 10 iaceii i ifpper a r i d lowe surfag sf 'i lf 7 2, thg anoii s ib may be oxidized, for example, including the inner surfaces of the apertures and the oxidation removed from the upper and lower surface by known methods. The insulating effect of the oxidation is sufficient to establish this difference in work fiinction.

Alternatively, for example, the cathodes may be fabricated by coating a thin metal sheet with a photoresist on both sides, photographically exposing the desired hole pattern, as known in the art etching out the apertures 80, treating the entire surface chemically with a suitable oxidant, as by spraying, to oxidize the inner surfaces 81 of the apertures 80, and then removing the photoresist by well-known methods.

It is apparent that any thin insulative coating applied to the apertured cathode and then removed from the outer surfaces or applied directly only to the inner surfaces of the apertures would achieve the desired result.

I claim:

1. In a cathode for use in common between two layers of gas cells in a display device wherein individual cells in each layer are interconnected by an aperture of very small diameter,

means on the inner surface of at least one of said apertures for increasing the work function of said surface relative to the outer surfaces proximate the ends of said aperture whereby said inner surface does not support cathode glow under working conditions of the interconnected cells.

2. The cathode of claim 1 wherein said means is a thin insulating coating.

3. The cathode of claim 2 wherein said insulating coating is an oxidized layer.

4. A display panel comprising:

at least one pair of gas cells having a cathode in common therebetween, said cathode having an aperture therein of not more than 3 mil diameter for interconnecting said pair,

means for maintaining cathode glow around said aperture in one of said at least one pair of gas cells, selective means for spreading said cathode glow into the other of said at least one pair of gas cells, and means on the inner surface of said aperture for preventing the spread of said cathode glow into said other cell in the absence of activation of said selective means.

i III k 

1. In a cathode for use in common between two layers of gas cells in a display device wherein individual cells in each layer are interconnected by an aperture of very small diameter, means on tHe inner surface of at least one of said apertures for increasing the work function of said surface relative to the outer surfaces proximate the ends of said aperture whereby said inner surface does not support cathode glow under working conditions of the interconnected cells.
 2. The cathode of claim 1 wherein said means is a thin insulating coating.
 3. The cathode of claim 2 wherein said insulating coating is an oxidized layer.
 4. A display panel comprising: at least one pair of gas cells having a cathode in common therebetween, said cathode having an aperture therein of not more than 3 mil diameter for interconnecting said pair, means for maintaining cathode glow around said aperture in one of said at least one pair of gas cells, selective means for spreading said cathode glow into the other of said at least one pair of gas cells, and means on the inner surface of said aperture for preventing the spread of said cathode glow into said other cell in the absence of activation of said selective means. 